The goal is to develop dispersive-fiber optics for in situ delivery of light in photodynamic therapy. A new method will be investigated for angularly dissipating light from the end of the waveguide. The objective is to design a dispersion approach suitable for very small fibers which is simple and practical to produce. The dispersive-fiber is intended for applications where small dimension is critical to accessing the tissue site and wide angle illumination is needed for efficient exposure and photo- therapy. In Phase I the feasibility of the method will be established using versions of fiber devices built to the model design. Light distribution around the fiber tip will be assessed. Design parameters producing best dispersion characteristics will be identified based on radial intensity profiles. The fibers will have application towards cancer treatment, other related forms of phototherapy, as well as in vivo fiber optic sensing.